CAUSALITY IN VISCOELASTICITY

• Main Author: Jack Dvorkin
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2005
• Subjects: Methane hydrate
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.524.4314; http://www.rocksolidimages.com/pdf/2005_QCausalityJD.pdf

In a viscoelastic sample, the causality principle links the attenuation of a stress wave to the changes in its speed as the frequency varies. This rigorous theoretical link helps explain the velocity-frequency dispersion and attenuation commonly observed in rocks with fluid. Usually, the attenuation is maximum in the frequency range where the velocity change is most rapid. Experiments indicate that a link between velocity change and attenuation persists even in cases where both are functions of a different variable, not necessarily frequency. This link can be observed in a sample as well as among several samples. The variables responsible for velocity dispersion and attenuation include the pore-fluid viscosity; temperature; confining and pore pressure; strain amplitude at the wave; water saturation; methane hydrate content; scale of inhomogeneity; and porosity. Perhaps a universal principle exists, not formulated as yet, that links velocity dispersion to attenuation for a multitude of underlying physical variables.